1). Field of the Invention
The present invention relates to a method for removing, and/or recovering fine size particles from a liquid carrying medium utilizing devices which separate under the influence of centrifugal force disposed within a vortex body, through the addition of polymeric additives The present invention also relates to a system for recovering fine size particles from the liquid carrying medium utilizing devices which separate under the influence of centrifugal force disposed within a vortex body. The method and system have particular applicability in the mineral aggregates industry, including, but not limited to; phosphate production, granite, sandstone, limestone, and igneous rock production. Additionally, alumina manufacture via the Bayer Process, and Titanium Dioxide manufacture via the Chloride Process, as well as waste neutralization tailings from the same Chloride/Sulfate process, may also utilize this method and system.
2). Description of Prior Art
The efficient and cost effective removal, and or recovery of very fine solids has presented many problems for various mineral and aggregate producers over the years. There are some uses for aggregate fines materials. Granite and sandstone and igneous fines can be recovered and added to existing base material production, or used in the ceramics industry. Ag-Lime can be used as a soil enhancer. However, it is necessary for these fines to be separated quickly and completely, and in a fairly tight specification, for addition to the existing stockpiles.
Hydraulic centrifugal separators, or cyclones/hydrocyclones have long been utilized to remove some of the larger particles in a fluid process stream. The primary disadvantage to these devices being the inability to remove very fine size solid particles without resorting to multiple small diameter units. Even then, these cyclonic vessels are typically unable to remove solids smaller than −325 mesh. Numerous attempts to add polymeric additive(s) prior to the cyclone have been disappointing. This is largely due to the extremely high vector forces inside the hydraulic centrifugal vessel shearing the flocculated particles.
The most common means of removing fines generated in the production process has been to hydraulically move the fine particle stream to a retention pond for gravity settling. Typically, some flocculating agent has been added to the stream as it enters the Pond to aid in settling even the very smallest particles. Water is pumped back to the process from these ponds.
If space permits, these ponds are allowed to fill with solids before being taken out of service and undergo evaporative drying, otherwise, they are cleaned while in service. This has involved the use of draglines, clamshells, and dredges to remove the partially dry solids. Then watertight trailers must be used to haul the material to a disposal area. This operation is quite costly, and disruptive to normal plant activities, additionally, manpower and machinery normally dedicated to production must be employed for this task.
Additional disadvantages to this system include the loss of water from the ponds due to evaporation,. Large pumps are required to transport the fines to the ponds, and then move water back to the plant area. Added electrical requirements are high.
In the case of beneficiation of Phosphate ore, the principle waste stream is a phosphatic clay which responds poorly to conventional liquid-solid separation techniques. Large-Scale Dewatering of Phosphatic Clay Waste From Northern Florida, Bureau of Mines Report of Investigations, 1985, details the extremely low settling rate of these clays-typically requiring several years for the material to thicken from 3% to 20%. The discharge of these clay wastes to settling areas can be as high as 200,000 gal/min. To accommodate these waste steams, huge impoundment areas must be constructed, ranging in size from 400–600 acres at a height of 40′.
The main reason for the slow settling of these clays is due to their make-up. Major constituents are apatite, quartz, montmorillonite and attapulgite, along with smaller amounts of kaolinite, illite, and dolomite. Several of these being “swelling” clays. Due to the very slow settling times, Evaporation of the water pumped to the ponds is significant, amounting to nearly 10% of the total volume, or 5 tons of water for every ton of phosphate produced.
Disadvantages for this system are many, including the large amount of land needed to accommodate the solids. Energy consumption for the many pumps to move the slurry through the dike system. Water consumption, especially in times of drought.
Additionally, new environmental permitting processes are becoming more stringent and costly to meet.
In the Bayer alumina process, aluminate liquor leaving the flashing operation contains from 2–20% solids. These solids consist of both insoluble products that precipitate during digestion, along with residue that remains after the reaction between bauxite ore and caustic. According to U.S. Pat. No. 4,767,540, in order to rapidly settle the finer solids particles from the liquor, a flocculant such as a hydroxamated polyacrylamide is added to the slurry. This slurry is then sent to very large Settling Vessels, where the overflow of “green” liquor still may contain from 10–100 mg/liter of suspended solids. These solids must be filtered from the liquor. Likewise, the “red mud” (settled solids) are withdrawn from the bottom of the Settler and passed through a countercurrent washing circuit for recovery of sodium aluminate and caustic soda.
The cost and space requirements for the Settlers is large, and requires several operators to oversee. Upsets in the Settlers can lead to large amounts of fines to be filtered. This significantly slows the process, thus increasing production costs. Fine solids escaping the filtration step can cause undesirable impurities such as iron or titanium in the final product.
In recent years, a number of fines treatment processes have been introduced to address these problems. Cyclone separators have been used to separate a variety of materials from each other in accordance with their relative densities. U.S. Pat. No. 2,377,524 references the use of cyclone separators to separate solid particles from liquids. Accordingly, a feed mixture containing solid particles is introduced into a separating chamber via one or more tangentially directed inlet adjacent to the large end of the separating chamber. A fluid vortex is thereby created. The centrifugal forces created by the vortex move the more dense solids outwardly to the wall of the separating chamber, while the less dense materials (liquid and solids), are brought to the center of the chamber-there to be carried along by an inwardly located helical stream which surrounds the axially disposed “air core”. The less dense components are discharged through the overflow outlet. The denser material continues to spiral along the interior wall of the hydrocyclone and eventually exit by the underflow outlet (apex).
A rotating screen apparatus, such as that described by U.S. Pat. No. 5,366,639 has been used to separate relatively course material (2.00 mm to 0.050 mm) from fine particles in a liquid stream.
U.S. Pat. No. 5,819,955 describes a hydrocyclone device that includes an axial feed inlet that may further contain an outlet orifice surrounded by many flexible sectors which, in turn, are composed of resilient material. The separating chamber may also contain riffles, or grooves, to aid in separation of several solid, or liquid fractions.
U.S. Pat. No. 5,843,315 describes a method for introducing feed into a sand screw, with the larger particles separated from the fine particle stream. The fine particle stream is then introduced into a hydraulic centrifugal separator, which removes most particles larger than 200 mesh. The fine particle overflow from the hydrocyclone is treated with a polymeric additive and sent to a thickening tank. The underflow stream from the thickening tank is then fed to a belt filter press unit. This material is then transported back to re-blend for incorporation in the base, or discarded.
Derrick Corp., Hi “G” Dryer product brochure, Bulletin 3000, presents a technology that consists of a high frequency, linear motion vibrating screen that is fed fine particles from a cluster (8, 12, or 24) 4″ hydrocyclones Typical recoveries of from 50–80% of the fine solids in the stream, with the rest traveling with the overflow to a holding pond. Solids are in stackable form @ 70–80% solids.
U.S. Pat. No. 6,238,579 details a new type of hydrocyclone that provides for discharge (exit) ports for exit fluid flow at or adjacent to one another on one end of a vortex separating body; an inlet port(s) disposed at one end of a separating body having discharge (exit) ports for exit fluid flow disposed or adjacent to one another at an opposite end of the separating body.
All of the aforementioned methods and devices suffer from several deficiencies:
1). None of the prior art incorporate polymeric additives to increase the size of fine particles introduced into the hydrocyclone unit.
2). The current technologies require several pieces of separation equipment. Space requirements are often large, and all require some type of supervision and maintenance. Additionally, these processes do not eliminate the need for a clarifier, thickening tank, or holding pond, since the fine solids cannot be removed within one piece of equipment.
3). The combinations of equipment required are quite costly.
4). Cost and power requirements are significant in some of the applications.
5). Dredging and Dragline operations are not eliminated, only reduced.
6). Dried particles must be transported back to re-blend before adding back to the base.
7). Polymer additions are still necessary in virtually all of the applications.
8). Equipment wear and tear is high, due to the abrasive nature of the fine solids.
9). Typical applications require that multiple small cyclones (4″) be employed to remove fine particles larger than 300 mesh. This requires that extra cyclones be purchased, exclusive of the cyclones already on location. Material smaller than 325 mesh is rarely removed by cyclones.
10). Some applications, such as titanium dioxide pigment productions, and aluminum “red mud” filtration cannot be economically performed using current cyclone technology, due to excessive fine particle carry-over.
The method and system of the present invention is designed to more effectively remove fine suspended particles from any number of process streams. The improvements forming the basis of the present invention lie in adding polymeric additives to said process streams prior to introduction into hydraulic centrifugal separator(s). Said hydraulic centrifugal separator(s) having been modified to improve fines removal efficiency. This treatment leads to dramatically reduced levels of suspended fine particles in the cyclone overflow when compared to existing technology. Such reductions in suspended fine solids can lead to lower equipment and space requirements, a decrease in energy requirements, along with recapture of valuable products. Additionally, maintenance of equipment is significantly lowered due to the lubricity imparted to the fine solid particles by the polymeric additives.